Fix orchestration discriminator in single-instance purge requests

[andystaples]

Summary

Fixes #276.

Set isOrchestration=True on PurgeInstancesRequest in both synchronous and asynchronous purge_orchestration() methods. The previously omitted Boolean defaulted to false, the entity discriminator. This corrects the wire request; it does not imply every backend previously rejected the request or failed deletion. Equivalent correction: microsoft/durabletask-go#165.

Add request-level regressions covering both core clients, both Azure Managed clients, both Azure Functions clients, and the Functions purge_instance_history() compatibility alias. Cover default recursion and explicit true/false overrides, deletion-count and three-state completion conversion, and unchanged RPC exception propagation. Polling, timeouts, completion semantics, and worker behavior are unchanged.

Update all three applicable Unreleased changelogs.

[Copilot]

Copilot review overview

🟢 Approval recommended

The targeted protocol correction is correct, comprehensively tested, and appropriately documented.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes #276 by correctly identifying single-instance purge requests as orchestration purges.

Changes:

• Sets isOrchestration=True for synchronous and asynchronous clients.
• Adds regression coverage across core and provider clients.
• Documents the fix in all applicable changelogs.

File	Description
durabletask/​client.py	Corrects both purge request paths.
tests/​durabletask/​test_purge.py	Tests requests, results, recursion, and errors.
tests/​durabletask-azuremanaged/​test_dts_purge.py	Verifies inherited Azure Managed behavior.
tests/​azure-functions-durable/​test_client_compat.py	Verifies Functions clients and compatibility alias.
CHANGELOG.md	Documents the core fix.
durabletask-azuremanaged/​CHANGELOG.md	Documents provider impact.
azure-functions-durable/​CHANGELOG.md	Documents Functions provider impact.

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[Bernd Verst (berndverst)]

Looks good. This corrects the orchestration discriminator in both client paths while preserving signatures, recursive defaults, result semantics, and RPC error propagation. Provider release coordination is documented, with no public API break or new Python-version requirement.